Monday, October 19, 2015

When sharing can be a problem

By Justin Fujioka

Growing up, we’ve always been taught to share. Sharing is a vital life skill. But in the case of traffic infrastructure, sharing isn’t always a good thing – especially when two high-volume surface streets share a single off-ramp.

After years of comments and suggestions from the public to improve traffic flow on westbound SR 520 in Redmond, a relatively inexpensive ($350,000) and quick fix is about to get underway. We received a lot of input, mainly through email, regarding the congested single-lane off-ramp to both Northeast 51st and Northeast 40th streets.

Here’s the problem: The off-ramp was designed about 25 years ago, before anyone had any clue about the exponential growth at the nearby Microsoft campus. In the morning, thousands of vehicles squeeze into one lane for two heavily used exits, creating a half-mile backup all the way to the merge area at the West Lake Sammamish Parkway NE on-ramp. Given the demand, a two-lane exit seemed like a way to help ease the congestion.

We received a wide array of ideas from the public and the one that stood out most to our engineers was to split the common exit to Northeast 51st and Northeast 40th streets into two separate off-ramps. Instead of physically widening the off-ramp and collector-distributor to two lanes, we settled on this more innovative plan to create a new exit a half-mile down the freeway. This will give us a two-lane exit capacity with two sequential off-ramps instead of one big one.

We decided on this solution mainly for logistics and cost-savings. You see, the mainline and collector-distributor have matching cross slopes and are separated by free-standing barriers. This means we can literally pick up a few barriers and move them to create a new exit. Creating one large two-lane off-ramp would have required building a new roadbed and drainage structures – costly steps we can skip!

Barriers will have to be placed just past the existing exit to Northeast 51st and Northeast 40th streets to close off the collector-distributor, creating an off-ramp for traffic going to Northeast 51st Street only. In addition, about 800 feet of barrier under the Northeast 51st Street overpass will be removed to create a new Northeast 40th Street exit from the mainline. A new gore point with an impact attenuator will be put in, along with new lighting, lane striping and overhead signs.

Drivers should plan ahead for lane and ramp closures, primarily in late October and early November. Contractor crews are scheduled to return to the area in January to complete the project. Most of the work is not expected to be louder than existing overnight background noise from SR 520.

Closure details:

Friday, Oct. 23, to the morning of Monday, Oct. 26 - Two right lanes of westbound SR 520 at Northeast 51st Street will be closed from 10 p.m. Friday to 5 a.m. Monday. The westbound SR 520 off-ramp to Northeast 51st Street/Northeast 40th Street will also be closed. A signed detour will be in place. This work is weather dependent.

Monday, Oct. 26, to Friday, Oct. 30 - The right lane of westbound SR 520 at Northeast 51st Street will be closed from 5 a.m. Monday to 10 p.m. Friday.

Friday, Oct. 30, to the morning of Monday, Nov. 2 - Two right lanes of westbound SR 520 at Northeast 51st Street will be closed from 10 p.m. Friday to 5 a.m. Monday. The westbound SR 520 off-ramp to Northeast 51st Street/Northeast 40th Street will also be closed. A signed detour will be in place. This work is weather dependent.

After this first round of closures, drivers will no longer share a single ramp to Northeast 51st and Northeast 40th streets. But that doesn’t mean they have to stop sharing just about everything else in life.

3 comments:

How about the eastbound 520 exit to 40th/51st? That backs up horribly most mornings around 9am and is complicated by the onramp from NB 148th Ave NE. There are many cars merging to the right into the backup from mainline 520 to get to the offramp, and many cars merging left into the backup from the 148th Ave onramp to cross over to mainline 520 EB. Is there any similar quick fix to alleviate the crossing traffic streams there?

Totally agree with Erik, the eastbound exits of NE40th backs up almost all the way to 148th. If you were to just remove the jersey barrier there it would eliminate the bottleneck at the NE40th exit allowing people to use the 40th or the 51st exits separately. Microsoft has built a lot of new buildings toward the 51st street exit especially with the new 83, 84 buildings. People could take the 51st exit to get to those buildings but can't due to the barrier. I sometimes have to just skip the entire 41st street exit and go down to West Lake Sammamish then up 40th to get to work due to the backup.